CN111272730B - High-sensitivity optical fiber surface plasmon sensor and preparation method thereof - Google Patents

Abstract

The invention discloses a high-sensitivity optical fiber surface plasmon sensor and a preparation method thereof, wherein the sensor comprises an optical fiber and a gold film arranged on the end surface of the optical fiber, the gold film is of a double-period gold disk array structure, and the double-period gold disk array structure is obtained by adopting nano PS microspheres with different diameters to sequentially perform ion etching on the surface of the gold film. The invention has the characteristic of double cycles, liquid to be measured is injected into the double-cycle gold disc structure, and the optical fiber is directly attached to the surface of the structure. The light source enters from the other end of the optical fiber or directly irradiates from the bottom, when the light source passes through the double-period gold disk array, a part of the light source is absorbed, and the laser generates a measurable Raman signal under the action of the metal structure. The invention can lead out the detection light from the light source through the optical fiber, interact with the sample, and send the signal light to the monitoring system through the collection and transmission of the optical fiber, has simple structure and is suitable for processing and production.

Description

High-sensitivity optical fiber surface plasmon sensor and preparation method thereof

technical field

The invention relates to the technical field of photochemical sensors, in particular to a high-sensitivity optical fiber surface plasmon sensor and a preparation method thereof.

Background technique

Surface plasmons (SPPs) are electromagnetic wave modes induced by the interaction of light and free electrons on metal surfaces. Its existence was first predicted by Rufus Ritchie in 1957. Later, with the continuous exploration of researchers, it was found that in the presence of the oscillating electromagnetic field of light, the free electrons of metal nanoparticles oscillated relative to the metal lattice. At this time, the intensity of the local light field around the nanostructure is greatly increased compared with the light field intensity of the incident light. This process is the resonance of light at a specific frequency, known as surface plasmon resonance (SPR). Since surface plasmon resonance was first used for real-time analysis of biological systems in the 1990s, it has become an important field in biochemistry, biology and medicine due to its real-time, label-free and non-invasive characteristics. Optical Biosensing Technology. However, due to the discontinuity of the metal hole array, the number of electrons on the metal surface will be greatly reduced, and the electric field enhanced at a fair wavelength will rapidly decay through the metal or dielectric interface. Surface Plasmon Resonance (LSPR).

In recent years, plasmonic biosensors utilizing nanoparticles and nanopore geometries have received extensive attention due to their ability to meet the needs. The first study of the optical properties of nanohole arrays by T. W. Ebbesen et al. showed that, under appropriate conditions, individual nanoholes in metal thin films may support LSPR in a similar manner, giving insights into how to control the motion of photons in the range of near electric fields. It provides a clear answer, and also provides a new way for people to use and control light. Subsequently, many studies at home and abroad conducted further discussions on several parameters affecting the projection enhancement effect, such as metal materials and periodic structures. Most of the structures are covered with a metal film in the nanopore array or fabricated on the substrate. However, the method of fabricating irregular hole arrays using multi-periodic structured nanoparticles is rarely involved and studied. With the continuous development of sensor technology, people's expectations for such structured sensors are getting higher and higher. Has a high application prospect.

Therefore, by directly attaching the optical fiber to the surface of the multi-period gold nanodisc array, the prepared optical fiber has extremely high sensitivity, and can quickly and accurately determine the presence of the measured substance from the spectrometer, which is more miniaturized, intelligent and convenient. It is mainly used in some important fields such as the detection of contraband at the airport and customs, the authenticity identification of the jewelry industry and the food industry.

SUMMARY OF THE INVENTION

The purpose of the present invention is to change the traditional circular hole array, provide a high-sensitivity optical fiber surface plasmon sensor and a preparation method thereof, and use nano-spheres to etch an irregular multi-period nano-hole array structure. , due to the SP excitation and coupling effect, a part of the light will be absorbed by the gold disk array, so the waveform appearing on the oscilloscope will appear sharp, antisymmetric peak-to-valley line shape, the same gold film can also be prepared with multiple different periods , forming multiple absorption peaks, showing brand-new optical properties, which can be used for optical sensing research.

For achieving the above object, the technical scheme provided by the present invention is:

A high-sensitivity optical fiber surface plasmon sensor, comprising an optical fiber and a gold thin film arranged on the end face of the optical fiber, the gold thin film is a double-period gold disk array structure, and the double-period gold disk array structure adopts different The diameter of the nano-PS microspheres was sequentially obtained by ion etching on the surface of the gold film.

The invention prepares the periodic nano gold disk array on the end face of the optical fiber. By 90°cutting or tapering the optical fiber, the external light is incident from the other end of the optical fiber and transmitted to the bottom of the patterned gold film through the optical fiber. The light of some frequencies can excite surface plasmons on the surface of the nanodisk array. At the same time, the energy of this part of the light is converted into surface plasmon, and the intensity of this part of the light reflected from the gold nanodisk decreases. By demodulating the reflected light, the wavelength of the excited surface plasmon can be obtained, thereby Real-time sensor detection and other applications.

Main working principle: When the light wave is incident on the metal surface, the free electrons will oscillate collectively on the interface with a small amplitude under the guidance of the light wave, and the collective composed of the free oscillating positive and negative particles is called Surface Plasmons (SPs) , however, there are multiple SP modes in such a gold nanodisc array. With the excitation of these SP modes, ideal transmission and reflection spectra can be obtained. Therefore, after the light source enters the fiber, due to the SP excitation and coupling effects, a part of the light will be absorbed by the gold disk array, so that the waveform appearing on the oscilloscope will have a sharp, antisymmetric peak-to-valley line shape. The same gold film can also prepare multiple patterns with different periods, forming multiple absorption peaks.

In order to optimize the above technical solutions, the specific measures taken also include:

The above-mentioned double-period gold disk array structure includes a first disk and a second disk; wherein, the first disk is prepared by etching large-diameter nano-PS microspheres with a gold film as a base, and the first disk is prepared by etching. The discs are tightly connected; the second disc is prepared by etching the surface of the first disc as a new substrate and is prepared by etching small-diameter nano-PS microspheres, and the second discs are tightly connected.

The diameter ratio of the large-diameter nano-PS microspheres adopted by the above-mentioned first disc and the diameter ratio of the small-diameter nano-PS microspheres adopted by the second disc is 2:1; wherein, in each group of the first discs, a A whole second disc at the center and six partial second discs evenly distributed in the circumferential direction of the center.

The above-mentioned gold film and the end face of the optical fiber are connected by electroplating or gluing.

The present invention also protects a method for preparing the high-sensitivity optical fiber surface plasmon sensor, comprising the following steps:

S1: Take the multimode fiber and cut it at 90° or taper it;

S2: A 50nm-thick gold film is arranged on the end face of the fiber that has been cut or taper-drawn by electroplating or gluing;

S3: Prepare two sets of colloidal solutions of polystyrene microsphere arrays with different diameters, and slowly inject the two sets of colloidal solutions onto the water surface to form ordered microsphere films A and B respectively;

S4: transfer the microsphere film A to the end face of the optical fiber obtained in step S2, put it into the ion etching sample chamber after natural drying, etch the nano-gold disc array on its surface, and then etch the nano-spheres on the surface;

S5: transfer the microsphere film B to the end face of the optical fiber obtained in step S4, put it into the ion etching sample chamber after natural drying, etch the nano-gold disk array on its surface, and then etch the nano-spheres on the surface layer, A high-sensitivity fiber-optic surface plasmon sensor with a double-period gold nanodisc array structure is obtained.

Further, in the step S2, the method of gluing specifically refers to attaching the gold film to the end face of the optical fiber by epoxy glue.

Further, in step S3, the ratio of the diameter of the polystyrene microspheres used in the microsphere film A to the diameter of the polystyrene microspheres used in the microsphere film B is 2:1.

Further, in the steps S4 and S5, the beam current used in the etching is 10-100 nm/min.

The invention has the characteristic of double period, the liquid to be tested is injected into such double period gold disc structure, and the optical fiber is directly attached to the surface of the structure. The light source enters from the other end of the fiber, or directly illuminates from the bottom. When passing through the double-period gold disk array, part of the light source will be absorbed, and the laser will generate a measurable Raman signal under the action of the metal structure. Raman spectroscopy refers to the phenomenon in which the frequency of light waves changes accordingly after scattering. It is a non-destructive analytical technique that can obtain detailed information on the chemical structure, phase and morphology, crystallinity, and molecular interactions of a sample. The position and intensity of spectral peaks in Raman spectra can directly reflect the content of substances, so the model can be simplified and the calibration of samples can be reduced. When gases, liquids and transparent samples are irradiated with a single color with a wavelength much smaller than the particle size of the sample, most of the light is projected as it was originally found, while a small part is scattered at different angles, resulting in scattering Light. When viewed in the vertical direction, in addition to the Rayleigh scattering with the same frequency as the original incident light, there are also a series of symmetrically distributed Raman lines that are slightly shifted from the incident light frequency. This phenomenon is called Raman spectroscopy. Mann effect. Due to the number of Raman spectral lines and the magnitude of the displacement, the length of the spectral lines is directly related to the vibrational or rotational energy level of the sample molecules. Therefore, similar to infrared absorption spectroscopy, the study of Raman spectroscopy can also obtain information about molecular vibrations or rotations. At present, Raman spectroscopy has been widely used in the identification of substances and the study of molecular structures.

The beneficial effects of the present invention are:

1. The present invention is to directly transfer a layer of the prepared PS microsphere array on the end face of the optical fiber plated with a layer of gold film after cutting, etch it, then remove the transferred PS microsphere array, and prepare the first layer of tight Linked periodic gold nanodisc structures. Next, transfer another layer of the prepared PS microsphere array on such a structure, the diameter of the PS microsphere at this time is half of the diameter of the PS microsphere transferred for the first time, and then etch and remove the spheres. External light is injected from the other end of the double-period structure optical fiber after the preparation, and transmitted to the bottom of the patterned gold film through the optical fiber, and its optical properties are detected and analyzed by a spectrometer. The structure is simple and easy to process and prepare.

2. In the existing measurement, the object to be measured must be placed in the measurement optical path in order to obtain a more accurate spectrogram. Compared with the prior art, the present invention can extract the probe light from the light source through an optical fiber, interact with the sample, and After the collection and transmission of the optical fiber, the signal light is sent to the monitoring system. The invention has a simple structure and is suitable for processing and production.

Description of drawings

FIG. 1 is a schematic diagram of the structure of the fiber end face after cutting or tapering according to the present invention.

2 is a schematic diagram of a large-diameter PS microsphere array prepared by spin-coating a layer on the end face of an optical fiber pasted with a gold film according to the present invention.

FIG. 3 is a schematic diagram of a gold disk array with a periodic structure formed after the large-diameter PS microspheres of the present invention are etched.

FIG. 4 is a schematic diagram of continuing to etch and remove the large-diameter PS microspheres on the surface, and then transferring a layer of small-diameter PS microspheres arrays in the present invention.

FIG. 5 is a schematic diagram of forming a gold disk array with periodic structure after etching in FIG. 4 .

FIG. 6 is a schematic diagram of the overall structure of the present invention for continuing to etch and remove small-diameter PS microspheres.

FIG. 7 is an enlarged view of the structure of the fiber end face of the present invention.

The serial number in the figure, 1-fiber, 2-epoxy glue, 3-gold film, 4-large-diameter nano-PS microspheres, 5-small-diameter nano-PS microspheres, 31-first disc, 32-second disc , 321 - the whole second disc, 322 - part of the second disc.

Detailed ways

The present invention will be further described below with reference to the accompanying drawings and embodiments.

A high-sensitivity optical fiber surface plasmon sensor, comprising an optical fiber 1 and a gold thin film 3 arranged on the end face of the optical fiber, the gold thin film 3 is a double-period gold disk array structure, and the double-period gold disk array structure It is obtained by using nano-PS microspheres of different diameters on the surface of the gold film 3 by ion etching in turn. Referring to FIG. 7, the double-period gold disk array structure includes a first disk 31 and a second disk 32; wherein, the first disk is composed of large-diameter nano-PS microspheres 4 and gold thin films 3 as The substrate is prepared by etching, and the first discs 31 are closely connected; the second disc 32 is based on the surface prepared by the first disc 31 as a new substrate and is etched by small-diameter nano-PS microspheres 5 etch preparation, the second discs 32 are tightly connected.

In this embodiment, the ratio of the diameter of the large-diameter nano-PS microspheres 4 used in the first disk 31 to the diameters of the small-diameter nano-PS microspheres 5 used in the second disk 32 is 2:1; The group of first disks 31 includes a whole second disk 321 located at the center and six partial second disks 322 evenly distributed in the circumferential direction of the center.

Example 1

A preparation method of a high-sensitivity optical fiber surface plasmon sensor, comprising the following steps:

S1: Referring to Figure 1, take the multimode fiber and taper it. The core of the multimode fiber is 200 μm and the cladding is 220 μm. After the taper process, the multimode fiber needs to be ground;

S2: Referring to Figure 1, a layer of 50nm-thick gold film is set on the end face of the optical fiber that has been taper-drawn by means of gluing. Specifically, epoxy glue 2 is used to paste the gold film on the end face of the optical fiber;

S3: Prepare two sets of colloidal solutions of polystyrene microsphere arrays with different diameters, and slowly inject the two sets of colloidal solutions onto the water surface to form an ordered microsphere film A and a microsphere film B respectively; among them, the microsphere film The diameter of the polystyrene microspheres used in A is set to 600 nm, as shown in Note 4 in Figure 2, and the diameter of the polystyrene microspheres used in the microsphere film B is set to 300 nm, as shown in Note 5 in Figure 4 for details. , the volume of the colloidal solution is 20 mL, the diameter deviation rate is 0.2%, the volume percentage concentration is 0.05%, and the solvent is deionized water;

S4: Referring to Figures 2~3, transfer the microsphere film A to the end face of the optical fiber obtained in step S2, and put it into the ion etching sample chamber after natural drying. min to 100 nm/min, which can be adjusted according to different needs), the surface of which is etched with nano-gold disc arrays, and then the nano-spheres on the surface are etched away;

S5: Referring to Figures 4 to 6, transfer the microsphere film B to the fiber end face obtained in step S4, put it into the ion etching sample chamber after natural drying, and select an etching rate of about 20 nm/min (the etching rate range is 10 nm/min min to 100 nm/min, which can be adjusted according to different needs), the surface of which is etched with nano-gold disc array, and then the surface layer of nano-spheres is etched to obtain a high-sensitivity optical fiber with double-period nano-gold disc array structure Surface plasmon sensor.

S6: The light source enters the other end of the optical fiber, and is transmitted to the bottom of the patterned gold film through the optical fiber, and the spectrum of the structure is monitored in real time by a spectrometer.

Example 2

A preparation method of a high-sensitivity optical fiber surface plasmon sensor, comprising the following steps:

S1: Take the multimode fiber and cut it at 90°. The core of the multimode fiber is 200 μm and the cladding is 220 μm. After 90° cutting, the multimode fiber needs to be ground;

S2: A 50nm-thick gold film is arranged on the cut fiber end face by electroplating;

S3: Prepare two sets of colloidal solutions of polystyrene microsphere arrays with different diameters, and slowly inject the two sets of colloidal solutions onto the water surface to form an ordered microsphere film A and a microsphere film B respectively; among them, the microsphere film The diameter of the polystyrene microspheres used in A is set to 600 nm, the diameter of the polystyrene microspheres used in the microsphere film B is set to 300 nm, the volume of the colloidal solution is 20 mL, the diameter deviation rate is 0.2%, and the volume percentage concentration is 0.05 %, the solvent is deionized water;

S4: Transfer the microsphere film A to the end face of the optical fiber obtained in step S2, and put it into the ion etching sample chamber after natural drying. , which can be adjusted according to different needs), the surface of which is etched with a nano-gold disc array, and then the nano-spheres on the surface are etched away;

S5: Transfer the microsphere film B to the fiber end face obtained in step S4, put it into the ion etching sample chamber after natural drying, and select the etching rate to be about 80 nm/min (the etching rate ranges from 10 nm/min to 100 nm/min). , which can be adjusted according to different needs), the surface of which is etched with nano-gold disc array and then the surface layer of nano-spheres is etched to obtain a high-sensitivity optical fiber surface plasmon sensor with double-period nano-gold disc array structure .

S6: The light source enters the other end of the optical fiber, and is transmitted to the bottom of the patterned gold film through the optical fiber, and the spectrum of the structure is monitored in real time by a spectrometer.

The above are only the preferred embodiments of the present invention. It should be pointed out that for those of ordinary skill in the art, some modifications and improvements can be made without departing from the inventive concept of the present invention, which belong to the present invention. the scope of protection of the invention.

Claims (5)

1. A high-sensitivity optical fiber surface plasmon sensor is characterized in that: comprising optical fiber (1) and a gold film (3) arranged on the end face of the optical fiber, and described gold film (3) is a double-period gold disk array structure, the double-period gold disk array structure is obtained by using nano-PS microspheres of different diameters on the surface of the gold film (3) through ion etching in sequence; The double-period gold disk array structure includes a first disk (31) and a second disk (32); wherein, the first disk is composed of large-diameter nano-PS microspheres (4) and gold thin films. (3) The substrate is prepared by etching, and the first discs (31) are closely connected; the second disc (32) uses the prepared surface of the first disc (31) as a new substrate and The small-diameter nano-PS microspheres (5) are prepared by etching, and the second discs (32) are tightly connected; The diameter ratio of the diameter of the large-diameter nano-PS microspheres (4) adopted by the first disc (31) to the diameter ratio of the small-diameter nano-PS microspheres (5) adopted by the second disc (32) is 2:1; wherein Each group of first disks (31) includes a whole second disk (321) located in the center and six partial second disks (322) evenly distributed in the circumferential direction of the center. 2. A high-sensitivity optical fiber surface plasmon sensor according to claim 1, characterized in that: the gold film (3) and the end face of the optical fiber (1) are connected by electroplating or gluing . 3. The preparation method of the high-sensitivity optical fiber surface plasmon sensor according to any one of claims 1 to 2, characterized in that, comprising the following steps: S1: Take the multimode fiber and cut it at 90° or taper it; S2: A 50nm-thick gold film is arranged on the end face of the fiber that has been cut or taper-drawn by electroplating or gluing; S3: Prepare two sets of colloidal solutions of polystyrene microsphere arrays with different diameters, and slowly inject the two sets of colloidal solutions onto the water surface to form an ordered microsphere film A and a microsphere film B respectively; the microspheres The diameter ratio of the polystyrene microspheres used in the film A to the diameters of the polystyrene microspheres used in the microsphere film B is 2:1; S4: transfer the microsphere film A to the end face of the optical fiber obtained in step S2, put it into the ion etching sample chamber after natural drying, etch the nano-gold disc array on its surface, and then etch the nano-spheres on the surface; S5: transfer the microsphere film B to the end face of the optical fiber obtained in step S4, put it into the ion etching sample chamber after natural drying, etch the nano-gold disk array on its surface, and then etch the nano-spheres on the surface layer, A high-sensitivity fiber-optic surface plasmon sensor with a double-period gold nanodisc array structure is obtained. 4 . The method for preparing a high-sensitivity optical fiber surface plasmon sensor according to claim 3 , wherein in the step S2 , the method of gluing specifically refers to attaching the gold film by epoxy glue ( 2 ). 5 . on the fiber end face. 5 . The method for preparing a high-sensitivity optical fiber surface plasmon sensor according to claim 3 , wherein: in the steps S4 and S5 , the beam current used in the etching is 10-100 nm/min. 6 .

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